It is necessary to measure the inner dimensions of a tunnel periodically to ensure that the dimensions have not changed so as to render the tunnel unsuitable for the use for which it was originally constructed. With respect to railway tunnels, it is necessary to measure them periodically to determine that there is sufficient clearance for trains and their loads to pass safely. Tunnels do not remain stable and their dimensions may change over time for a number of reasons. The first is that deteriorating and unstable revetments of the tunnel lining may move inward with time. Another reason is that unstable geological conditions in the formations through which a tunnel was constructed may change the tunnel dimensions. Also, traffic demands may require that larger loads be carried than was originally contemplated. Before a larger load configuration can be assigned to a route, the tunnels involved in the route must be measured to ascertain that adequate clearance exists for the larger load. Also, the increased velocity of modern trains results in greater sway of the cars comprising the train. Tunnels must be measured to ensure they have adequate clearance for high speed trains.
A traditional means of measuring the inner dimensions of a tunnel is to erect a template having the minimum permissible dimensions on a rail inspection car and to make visual observations of the clearance between the tunnel wall and the template as the inspection car travels through the tunnel. This is time consuming and burdensome. Inspection cars also exist with templates having mechanical fingers that can detect contact with the tunnel wall. The fingers are fitted with electrical switches which activate lights on a display panel in the cab when the fingers contact a protrusion on the tunnel wall. This procedure is also time consuming and burdensome since it requires the operator to back up the inspection car and manually examine each detected protrusion.
U.S. Pat. No. 449,920 discloses a rotatable wooden arm used for measuring the inner dimension of a tunnel. The disclosed arrangement is stationary and can measure the inner dimensions of only one tunnel location at a time. U.S. Pat. No. 4,049,954 discloses the use of supersonic waves for measuring the inner dimensions of metallic tubes and the like. U.S. Pat. No. 4,291,579 discloses an inspection device for testing nuclear reactor vessels by means of an apparatus mounted on a track. The disclosed arrangement comprises a testing device mounted on a track utilizing ultrasonic test heads. The test heads are mounted at eight equally spaced points.
U.S. Pat. No. 4,571,848 discloses apparatus for measuring the transverse dimension of a drill hole and its geological formation. This invention is directed to bore holes such as oil and gas bore holes which may undergo diameter changes over time. The invention utilizes a three legged centering device provided with an electrical/hydraulic drive having extending or retracting the legs. United Kingdom Pat. No. 2,125,966 discloses an ultrasonic transducer arrangement which is utilized for the measurement of inner dimensions of pipes and tubes.
It may be seen from the above, that the currently available facilities for measuring and inspecting the inner dimensions of tunnels leaves much be desired since they do not provide for the measurement of tunnel dimensions by use of modern day technology and techniques. Instead, the currently available facilities are slow, time consuming and rely on manual arrangements or visual observation techniques. While the last four above-mentioned patents do provide for the measurement of the inner dimensions of cylindrical objects, such as pipes, they do so in a manner and with the use of facilities that are not applicable to the facile measurement of railway tunnels at the high speeds required by modern day railway systems.
In summary, it may therefore be seen that it is a problem to efficiently generate and collect data pertaining to the inner dimensions of railway tunnels.